1. Field of the Invention
The present invention relates to the field of magnetic resonance, particularly to the field of magnetic resonance imaging, and specifically, to an apparatus for transmitting magnetic resonance signals in MRI-monitored medical equipment.
2. Description of the Prior Art
Various forms of therapeutic treatments can be applied to the body of a human or other mammalian subject by applying energy from outside the body. For example, when treatments are performed by using hyperthermia techniques, ultrasonic or radio frequency energy is applied externally to a subject's body to heat different tissues. This is known as the high intensity focused ultrasonic knife (HIFU) technique. The working principle of the technique is that high-energy ultrasonic waves are emitted without contact and enter a human body via a water medium coupling. The applied energy can be focused to a very small spot within the human body so as to heat the tissues at that spot to a temperature sufficient to create a desired therapeutic effect, and to necrotize tissue at the focal spot within a very short period of time. This technique can be selectively used to destroy unwanted tissues within a body. For example, tumors or other unwanted tissues can be destroyed by applying heat, and the applied heat can heat the abnormal tissues to a temperature sufficient to kill them without damaging normal tissues nearby, with the temperature usually between 60° C. to 80° C. Such a process is commonly referred to as “thermal ablation”. Other hyperthermia treatments include selectively heating tissues so as to selectively activate a drug, or to promote some other physiological changes in a selected part of the body of a subject under the treatment. In other therapeutic methods, the applied energy can be used to destroy abnormal objects or deposits within a body such as, for example, in ultrasonic lithotripsy.
Magnetic resonance can be used in medical imaging for diagnostic purposes. In magnetic resonance imaging (MRI) procedures, a body region of the subject to be imaged is subjected to a strong magnetic field. Radio frequency (RF) signals are applied to the tissues of the subject within the imaging volume, and under these conditions, atomic nuclei are excited by the applied radio frequency signals and emit faint radio frequency signals, which are referred to as magnetic resonance signals. By superimposing appropriate gradients on the magnetic field during the procedure, the magnetic resonance signals can be obtained selectively from a limited region, such as a two-dimensional slice of the subject's tissue. The frequency and phase of the signals from different parts of the slice can be made to vary with their positions in the slice. By using this known technique, it is possible to demodulate the signals arising from different parts of the slice, and to deduce from these signals the properties of the tissues at each point of the slice.
Various proposals have been made to use magnetic resonance to monitor and guide medical equipment, particularly during a procedure of applying energy into a body. Certain magnetic resonance procedures are temperature sensitive, so that magnetic resonance data acquired by using these procedures will generate an image in a MRI system, and indicate temperature changes in tissues, so as to accomplish a therapeutic procedure. However, there are always some problems when such medical equipment is used in conjunction with an MRI system. Taking a HIFU treatment device as an example, during the MRI imaging procedure, RF signals are usually transmitted into a human body by a large body coil and this large body coil receives magnetic resonance signals emitted from the human body, and the MRI system makes use of these magnetic resonance signals to generate an image. When using medical equipment such as HIFU which requires very high precision imaging, the signal-to-noise ratio during the imaging by such a large body coil does not meet the requirements (the imaging quality of the body coil is not very high due to the fact that the coil is too large, and the bigger the coil is, the less ideal is the imaging quality). Therefore the local imaging quality is not high. An alternative is to acquire the magnetic resonance signals using a fixed receiving coil (local coil), but there are many restrictions in practical application. Since a fixed coil needs to be placed in HIFU solution in order to receive the magnetic resonance signals emitted from the body, and the fixed coil also needs to be connected to a cable and to transmit the magnetic resonance signals to the MRI processor for imaging, there is the problem of sealing the coil and the cable. Moreover, the need to seal the cable and the fixed coil in turn creates the problem of inconveniency in moving the fixed coil, which further results in a restriction to imaging range. All these problems are difficulties encountered when using the fixed coil.